The present invention relates to a thermoelectric conversion element utilized for performing thermoelectric power generation by the Seebeck effect or thermoelectric cooling (electronic cooling) by the Peltier effect, a manufacturing method for the thermoelectric conversion element, and a thermoelectric conversion module provided with the thermoelectric conversion element.
Conventionally, as an example of the thermoelectric conversion module utilized for performing thermoelectric power generation or thermoelectric cooling, a planar thermoelectric conversion module having a structure in which a plurality of p-type elements composed of p-type thermoelectric material and a plurality of n-type elements composed of n-type thermoelectric material are two-dimensionally arranged is known. In such a planar thermoelectric conversion module, a plurality of electrodes are provided on both a top face and a bottom face of the module, and one of the p-type elements and one of the n-type elements are electrically connected to each other via each of the electrodes. Thus, the plurality of p-type elements and the plurality of n-type elements are alternately connected in series.
When a temperature difference (temperature gradient) is applied on a top face side and a bottom face side of such a thermoelectric conversion module, the p-type element has a high potential on a low temperature side and a low potential on a high temperature side, while the n-type element has a high potential on a high temperature side and a low potential on a low temperature side. As a result, an electric current flows from the p-type element to the n-type element on the low temperature side, and an electric current flows from the n-type element to the p-type element on the high temperature side.
By the way, the above-described p-type element and n-type element were conventionally manufactured by melting or sintering a raw material composition having the same composition as that of the p-type thermoelectric material and the n-type thermoelectric material; cutting out block-shaped molded articles from the melted or sintered composition by mechanical processing (cutting processing); and arranging the obtained molded articles on a substrate and connecting the arranged articles in series.
However, since the thermoelectric material is likely to have a low mechanical strength, minute precision processing was difficult to be conducted, and reduction in size and thickness was difficult to be achieved. Also, there was a problem that yields come to be low in the cutting out processing of molded articles.
Furthermore, when a thermoelectric material having excellent thermal conductivity is utilized and an element cut out into a block shape is used, even if a large temperature difference is applied to the top and bottom faces of the thermoelectric conversion module, heat is easily transmitted to an inside of the element. Therefore, there was another problem that a sufficient temperature difference is not developed between both ends of the element.
Japanese Patent No. 4524382 proposed that a shape of the element is devised so that a large temperature difference between both ends of the element can be developed and that reduction in size of the thermoelectric power generation module can also be realized.
In Japanese Patent No. 4524382, at least one of the p-type and n-type elements has a shape of a plurality of spheres combined, and a narrowed portion having the smallest cross-sectional area is formed in a connection part of the neighboring spheres. By using such an element, heat flux is delayed at the narrowed portion, so that heat becomes more difficult to be transmitted between both ends of the element than in the case of the element cut out into a block shape. Accordingly, the temperature difference between both ends of the element becomes larger, thereby enabling improvement of the thermoelectric conversion performance of the thermoelectric conversion module.
Also, if the performance (electromotive force) of each element is improved as described above, the required performance can be ensured even with a smaller element. Therefore, the weight, thickness, and size of the thermoelectric conversion module can be reduced.